Electron microscopy (EM) is an essential tool in present day biomedicine. Investigators often must provide EM evidence to support conclusions reached by other approaches. Recent advances in instrument design for high pressure freezing (HPF), one of the greatest advances in EM since the introduction of glutaraldehyde fixation, now allow HPF preservation of cellular ultrastructure to be more widely applied to a variety of cellular specimens in more labs. The superiority of preservation of ultrastructural detail in samples prepared by HPF freezing coupled with freeze substitution fixation (FSF) is readily evident, and this method is becoming the standard fixation method for EM. The goal of this proposal is to obtain funds for the purchase of a Leica EM PACT2 high pressure freezer, a Leica EM AFS freeze substitution instrument, and a Leica Microbiopsy Transfer System. This equipment will be housed in the EM Core Facility at City of Hope (COH) and will primarily be used by six Major Users and four Minor Users, many of whom have R01 or other NIH funding. Many of the Major Users study cancer and are engaged in translational research focused on moving therapies from animal models to patients. They recognize the importance of optimal preservation of ultrastructure and have an increasing need for ultrastructural localization in their work. Some of these projects require immunolabeling for ultrastructural localization of molecules that could be lost or redistributed during conventional specimen preparation. Others need to distinguish endosomal and autophagic vesicles, organelles that are particularly sensitive to distortions during conventional sample preparation. The COH EM Core Facility was renovated in 2003, and was updated with new FEI Tecnai transmission and FEI Quanta ESEM scanning electron microscopes. We currently have a Leica cryo-ultramicrotome, and components for electron tomography and cryo-electron microscopy are being installed. The Leica EM PACT2 high pressure freezer, freeze substitution instrument, and microbiopsy transfer system will ensure that COH investigators have access to the most current fixation techniques for EM, which will greatly benefit their research on the prevention and treatment of cancer. Public Health Relevance: Contemporary medicine needs drugs that are rationally designed for specific interventions in cellular activities gone awry. Increasingly, biomedical research focuses on sub-cellular and macromolecular events to understand the details of cellular activities. The requested state-of-the- art Leica EM PACT2 high pressure freezer, Leica EM AFS freeze substitution instrument and Leica Microbiopsy Transfer System will aid NIH-funded investigators at City of Hope in developing novel therapies for cancer and other life-threatening diseases.